The invention relates generally to electrically controlling selected properties of a fluid and in particular, to a method and apparatus for electrically controlling selected properties of a colloidal suspension containing elongated fibrous particles.
It is well known that various properties of fluid compositions can be controlled by the application of external electromagnetic fields across the fluid. Thus, for example, electric fields can be applied across liquid crystals for changing their optical properties. Also, ferrofluidic preparations can have a varying viscosity upon the application of selected magnetic fields. Similarly, in accordance with the so-called Winslow effect, a dielectric fluid containing selected, small particles of a given density (often called an "electroviscous" fluid) will, upon the application of an electrical field, take on different viscous properties. The Winslow fluids are typically liquid dielectrics containing electrically conducting or electrically non-conducting, particles of substantially spherical shape. Apparatus employing the Winslow effect has been proposed for use in and with alternating-field chucking devices. And, similarly, ferrofluidics has found substantial use in clutching apparatus and in other fields.
Many workers in the field have used electroviscous fluid compositions because the electrical field can be easily applied across a fluid. This is contrast to the relative difficulty of applying magnetic fields of substantial strength across the fluid. Such magnetic fields require relatively large electric currents and substantial electrical circuits (for example large coil windings) for effecting the proper response in the fluid. Nevertheless, the results using electroviscous fluids have not been satisfactory.
Among the problems found in connection with the Winslow-type electroviscous fluids have been short shelf life and excessive sensitivity to heat. While efforts have been undertaken by some workers in the field to both provide a longer shelf life and less sensitivity to heat, there remain problems using fluids having a high density of particles.
Thus, while electromagnetic field response fluids have been used in many mechanical applications, electroviscous fluids have not been commercially successful. Further, there have not been proposed other advantageous uses of such electric field response fluids, for example, in the optical areas.
Accordingly, therefore, a primary object of the invention is the application of electromagnetic field response fluids to the control of electromagnetic radiation in wavelengths from the visible to the microwave regions of the electromagnetic spectrum. Other objects of the invention are a method and apparatus for controlling properties of a fluid for affecting mechanical and electromagnetic properties of the fluid. Further objects of the invention are a method and apparatus for affecting the mechanical and optical properties of a fluid by applying easily generated electrical fields across the fluid. Yet another object of the invention is a method and apparatus which is easy to implement and control for changing the mechanical and optical properties of a fluid, which are reliable, and which provide both mechanical and optical control states within the fluid in response to an applied electrical field.